The instant invention relates to a lattice production line and method of operating such a line.
Effectively operating an automated assembly line requires the solution of a number of problems. First, it is desirable to achieve maximum throughput efficiency. Second, the production line should have the ability to efficiently recover from a breakdown or failure of one or more of the elements of which the line is comprised so as to recover as soon as possible after a work station breakdown or task disruption. Third, it is desirable to maximize concurrency. Solutions to these three problems enables one to utilize as many robot assemblers simultaneously as possible in order to maximize throughput efficiency which, in itself, introduces the additional problem of preventing and recovering from deadlocks, wherein the production line, in essence, becomes jammed.
As a general approach to solving these problems, the patent literature includes a number of references wherein conveyor belts convey workpieces to and from turntables in order to direct workpieces through a manufacturing operation. In U.S. Pat. No. 3,530,571, workpieces on pallets are directed through a number of work stations while being queued on selected conveyor belts. However, the system in this patent is not suitable for the parallel processing of workpieces, wherein manufacturing operations are performed at turntable locations. Other patents, such as U.S. Pat. No. 4,480,738, disclose workpiece storage and shuttle apparatus; however, they do not disclose turntable arrangements. U.S. Pat. No. 4,515,264 discloses an array of four turntables connected to one another by orthogonal pairs of parallel conveyors. However, the turntables do not have storage facilities which are indexable and do not include independently indexable central areas. U.S. Pat. No. 4,291,797 discloses a pallet changer for a manufacturing plant, wherein a turntable selectively aligns with a number of conveyors. However, this alignment is for purposes of distribution among conveyors, rather than facilitating manufacturing steps performed at the conveyors so as to provide a lattice manufacturing system. Other patents of similar significance are U.S. Pat. Nos. 4,326,624 and 4,014,428, which also disclose turntables in combination with aligned conveyor belts. Lattice systems such as that proposed in the article by Cai et al., "Petri-Nets for Robot Lattices," Proceedings of the 1987 I.E.E.E. International Conference on Robotics and Automation. March-April 1987, Vol. 2, pp. 999-1004, suggests an arrangement for achieving maximum interconnectivity. But to yield maximum flexibility for the rerouting of tasks upon the occurrence of a station failure requires that each station have additional degrees of flexibility not provided by the prior art. In view of these and other considerations, there is a need for production lines which can take full advantage of assembly robots and other manufacturing robots, wherein a lattice is provided allowing for maximum throughput of workpieces with allowance for work station failure that does not shut down or hobble the entire assembly line.